This invention relates to removing carbonaceous impurities from zinc oxide. In one of its aspects, this invention relates to the oxidation of carbonaceous contaminants. In another of its aspects, this invention relates to an improvement in the process for preparing terephthalic acid from benzoic acid using zinc benzoate catalyst.
In the process disclosed in U.S. Pat. No. 3,873,609 for making terephthalic acid from benzoic acid using zinc benzoate catalyst, incorporated herein by reference, the catalyst is decomposed to zinc oxide by contact with quench water on the outlet of the reactor. This zinc oxide is insoluble in the effluent stream and eventually emerges in the process along with carbon residue to be slurried with terphenyl and passed to reaction with molten benzoic acid to be regenerated as zinc benzoate catalyst. In such a recycled system, there is a constant build-up of carbonaceous contaminant which must be removed to prevent interference with the reaction and coloration of product made with contaminated catalysts.
It is well known to remove the carbon contaminant by filtering the zinc benzoate solution. It has been found, however, that such a filtration is very difficult. It must be performed at temperatures above 300.degree. F. because the terphenyl in which the zinc benzoate is dissolved solidifies well above room temperature. Filter blinding on this operation can be a major problem.
The present invention has been found to solve the problem of removal of carbonaceous contaminant from zinc oxide.
It is therefore an object of this invention to provide a method for removing carbonaceous contaminant from zinc oxide. It is another object of this invention to provide a process for the recycle of zinc oxide for the preparation of zinc benzoate with an efficient and economical removal of carbonaceous contaminant.
Other aspects, objects and the various advantages of this invention will become apparent upon reading the specification and the appended claims.